The present invention relates to the encoding and decoding of data in a particular data format for incorporation in a Vertical Blanking Interval (VBI) of an NTSC compatible (or other type) video signal, for example.
A number of video encoding systems convey ancillary digital data (for captions, sub-text, control functions and other purposes) in a Vertical Blanking Interval (VBI) of an analog video signal such as an NTSC compatible (or other type) video signal, for example. These systems employ data formats with specific preliminary signals for use in synchronizing to the ancillary data. The data formats also use specific data bit widths, timing and other characteristics that affect the recovery of the ancillary data in a video receiver decoder. A data format defined by IEC 61880 (1998 edition) entitled xe2x80x9cVideo and accompanied data using the vertical blanking intervalxe2x80x94Analogue interfacexe2x80x9d, clause 3 defines a VBI data signal with a preliminary sinusoidal synchronizing signal and a two bit (a logic one followed by a logic zero) reference pulse sequence followed by twenty bits allocated for conveying data. Similarly, ELAJ CPR-1204-1 entitled xe2x80x9cTransfer Method of Video ID information using Vertical Blanking Interval (525P system)xe2x80x9d defines a VBI data signal that omits a preliminary sinusoidal synchronizing signal but incorporates a two bit (a one followed by a zero) reference pulse sequence followed by thirty bits allocated for conveying data. The characteristics of these (and other) known VBI data formats impose constraints on the operation of a video receiver for receiving and decoding ancillary data conveyed in the VBI portion of an analog video signal. Specifically, such constraints limit the flexibility of decoder operation and the ability of a decoder to adaptively operate in different modes for decoding input video signals encoded to different video standards.
The problems imposed by such constraints and derivative problems, are addressed by a system according to principles of the invention.
A communication data format conveys digital ancillary data in a vertical blanking interval of a video signal. The format employs a reference symbol including a plurality of digital pulses for indicating the start of the ancillary data and also includes a header byte following the reference symbol. The header byte contains an identifier identifying a destination service for a payload of the ancillary data or an address identifying a destination of the payload. The format also conveys multiple payload bytes, following the reference symbol in which individual bits have a period substantially comprising a first integral multiple of a first clock period associated with a first data format, and a different second integral multiple of a second clock period associated with a second data format.